This invention relates to a receiving satellite switching apparatus used at a receiving station for satellite communication. More particularly, the invention relates to a receiving satellite switching apparatus for receiving radio waves, which are transmitted from two or more satellites, from a multibeam antenna, and inputting a predetermined polarized-wave signal, which is from a prescribed satellite, to the tuner of a CS receiver (communication satellite receiver).
In recent years, satellites for civilian use have been launched to make possible CATV utilizing satellites, as well as satellite communication in private industry. A large number of private receiving stations have been established as a result. Among these, private receiving stations which employ a multiple-type antenna for accommodating a plurality of satellites, rather than single antenna for accommodating a single satellite, have become increasingly popular owing to reduced installation expenses and advantages in terms of installation space.
FIG. 1 is a block diagram illustrating the construction of a single-type TVRO (television receiver-only system), which is one type of satellite communication receiving station. The system includes a single antenna 1 for receiving radio waves from a satellite, an ortho-mode transducer (OMT) 2 for separating the radio waves (circularly polarized waves) received by the antenna 1 into a V-polarized signal and an H-polarized signal, and low-noise block converters (LNB) 3a, 3b for amplifying each of the polarized signals by respective internal low-noise amplifiers and then converting the amplified signals into prescribed intermediate-frequency signals by frequency converters and inputting these signals to a CS receiver 5 via respective coaxial cables (IF cables) CB1, CB1'. LNB power supplies 4a, 4b supply DC voltage of +15 V to the low-noise block converters 3a, 3b, respectively, with the internal conductor of each coaxial cable serving as the + side and the external conductor as the - side. The CS receiver 5 accepts the polarized signals from the low-noise block converters 3a, 3b as input signals, selects and detects the signal of a prescribed channel of a prescribed polarized signal and outputs this signal that has been selected and detected. The system further includes a video unit 6, such as a TV or other video device. In the arrangement described above, a V/H changeover switch (not shown) is built in the CS receiver 5. However, as indicated by the dashed line, an alternative arrangement can be adopted in which a V/H changeover switch 7 is provided on the output side of the low-noise block converters 3a, 3b and is adapted to select the prescribed polarized signal and input it to the CS receiver 5 in response to a changeover signal from the CS receiver 5.
In accordance with this single-type TVRO, the V/H selection is simply carried out within the CS receiver or by an external switch. However, since a single-type TVRO is required for every satellite, multiple-type TVROs are becoming more popular.
FIG. 2 is a block diagram showing the construction of a multiple-type TVRO. This system includes a multibeam antenna 11 for receiving radio waves (circularly polarized waves) from a plurality of satellites (satellites Nos. 1 and 2), an ortho-mode transducer (OMT) 12a for separating the radio waves received from satellite No. 1 by the multibeam antenna 11 into a V-polarized signal and an H-polarized signal, an ortho-mode transducer (OMT) 12b for separating the radio waves received from satellite No. 2 by the multibeam antenna 11 into a V-polarized signal and an H-polarized signal, and low-noise block converters (LNB) 13a.about.13d for amplifying polarized signals V1.about.H2 from each of the satellites by respective internal low-noise amplifiers and then converting the amplified signals into prescribed intermediate-frequency signals by frequency converters and inputting these signals to a CS receiver 17 via coaxial cables (IF cables) CB11.about.CB14. The system further includes a polarized-signal selecting switch 14 for selecting the V-polarized signal or the H-polarized signal, a satellite selecting switch 15a for selecting the V-polarized signal from satellite No. 1 or No. 2, and a satellite selecting switch 15b for selecting the H-polarized signal from satellite No. 1 or No. 2. An LNB power supply 16 supplies DC voltage of +15 V to the low-noise block converters 13a.about.13d conforming to the combination of the selected satellite and polarized signal via the coaxial cables CB11.about.CB14. The CS receiver 17 selects and detects the signal of a prescribed channel of the inputted polarized signal and outputs the signal that has been selected and detected. The system further includes a video unit 18, such as a TV or other video device.
The system is provided with a changeover unit 19 the front panel of which has a V/H selection dial 19a and a satellite selection dial 19b. The arrangement is such that a voltage of .+-.15 V is inputted to the selection switches 14, 15a, 15b via control cables L1, L2 in dependence upon the dial positions. The changeover unit 19 is installed indoors along with the CS receiver 17 and video unit 18, etc. The other equipment is installed outdoors.
In a case where it is desired to receive a prescribed channel of the V-polarized signal of satellite No. 1, the dials 19a, 19b of the changeover unit 19 are manipulated to select "No. 1" and "V", whereupon +15 V is applied to the selection switches 14, 15a, 15b via the control cables L1, L2, so that the switches attain the states shown in FIG. 2. As a result, +15 V is fed to the low-noise block converter 13a from the LNB power supply 16 so that the V-polarized signal of satellite No. 1 whose frequency has been converted by the low-noise block converter 13a enters the CS receiver 17. A similar operation is performed when the H-polarized signal of satellite No. 1, the V-polarized signal of satellite No. 2 and the H-polarized signal of satellite No. 2 are selected.
In this multiple-type TVRO according to the prior art, one IF cable between the indoor equipment and the outdoor equipment is sufficient. However, three or more selection switches are required in order to perform the satellite selection and the V/H selection. Furthermore, the cables L1, L2 for switch control also are necessary between the indoor equipment and the outdoor equipment. As a result, the system has a complicated construction and therefore readily malfunctions and is not easy to maintain.
Another problem with the conventional multiple-type TVRO is that the selection switches assume intermediate positions unless they are provided with the voltage of .+-.15 V from the changeover unit, thereby making it impossible to perform the satellite selection and the V/H selection.
Still another problem is that since the conventional multiple-type TVRO requires the cables L1, L2 for switch control, the cost of installation is high.